Ring crystalline body and production method thereof

ABSTRACT

To provide a ring crystalline body, which is a ring crystalline body with a small diameter and formed with a thin line and capable of providing electric conduction along the ring, and to provide a production method of the ring crystalline body. A droplet is stuck to a surface of a substrate and then the droplet is evaporated to a discontinuous underlayer ring having an ultrafine three-dimensional structure on the substrate surface. After that, when a transition metal dichalcogenide, a transition metal trichalcogenide, or a low-dimensional conductor as raw material gas is evaporated, a ring crystalline body comprising the raw material is grown along the underlayer ring.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a ring crystalline bodycomprising a circularly continuous crystalline material and a productionmethod thereof and particularly relates to a finely ring crystallinebody impossible to be produced by a conventional etching method and aproduction method thereof.

[0003] 2. Description of the Related Art

[0004] A transition metal dichalcogenide (MX2) or a transition metaltrichalcogenide (MX₃), which is a compound of a transition metal (M) anda chalcogen (X=S, Se, Te), has drawn attention since it has beenconfirmed that the substance has a variety of electric and magneticproperties of from an insulator, a semiconductor, a semimetal, to ametal and from ferromagnetic, anti-ferromagnetic properties to Pauliparamagnetism.

[0005] Further, corresponding to the anisotropy of the crystal structureand the electron structure of the substance, a low-dimensional conductorwhich is a compound showing a high electric conductivity in theone-dimensional or two-dimensional direction, has the followingcharacteristics: its property is transformed (Peiers transition) from ametallic property to an insulator at a low temperature; the maximumelectric resistivity appears at a low temperature and owing to it, superperiod lattice strain (electric charge density wave) is caused: and Kohnanomaly, that the modulus of elasticity is considerably lowered bylattice vibration in specified cycles, takes place. A low-dimensionalconductor having these characteristic physical properties, which ageneral three-dimensional conductor of such as a metal does not have,has been expected to be applied for a variety of fields.

[0006] Further, the crystalline body comprising a continuously circularcrystalline ring is used as, for example, a superconducting quantuminterference device (SQUID). The SQUID is a superconductor-basedmagnetic sensor with high sensitivity and is capable of measuringextremely ultrafine magnetic flux density as extremely low as 10⁻¹⁵ to10⁻¹² T by using Josephson device in which a superconductor is weaklybonded and the SQUID is used for measuring the magnetic field generatedfollowing the activities of living bodies.

[0007] The ring crystalline body to be used for the SQUID hasconventionally been produced by forming a thin film comprising athree-dimensional conductor with a prescribed size on the surface of asubstrate by a conventional thin film production method and etching thethin film in ring-like shape.

[0008] In the production of SQUID, it is made possible to form a finering with the diameter of about several μm owing to the progress of theetching technique. However, even although the present etching techniquemakes it possible to narrow the diameter of the ring, it can make theline width of the ring at thinnest about 100 nm and further thinnerwidth has therefore been expected. Also, the method of etching the thinfilm has a problem that the method is accompanied with much waste tomake it difficult to reduce the cost.

[0009] Further, it has been well known that a superconductive materialsuch as NbSe₃ which is one of the above described transition metaltrichalcogenide and one-dimensional conductor, NbSe₂ which is one of thetransition metal dichalcogenide and two-dimensional conductor, and thelike can be obtained in forms of thin-film like or whisker-likecrystals. In the case that a ring crystalline body is produced byforming a thin film comprising NbSe₃ or NbSe₂ and then etching the film,the obtained body is a low-dimensional conductor, so that electricconductivity along the ring cannot be obtained and it means that theobtained ring crystalline body is impossible to be used for a SQUID, forwhich electric conductivity along a ring is essential. Consequently, aring crystalline body comprising a three-dimensional conductor hassolely been used for a SQUID.

[0010] However, taking the capabilities as a superconductor intoconsideration, a one-dimensional conductor as well as a two-dimensionalconductor is preferable as compared with a three-dimensional conductor.If it is possible to obtain a ring crystalline body of such alow-dimensional conductor having electric conductivity along the ring,it is expected that the capabilities of a SQUID are further improved.Moreover, a one-dimensional conductor, a two-dimensional conductor, anda three-dimensional conductor respectively have different manners tohave superconductivity and a ring crystalline body comprising alow-dimensional conductor is therefore supposed to be useful forpurposes other than a SQUID.

SUMMARY OF THE INVENTION

[0011] Hence, an object of the present invention is to obtain a ringcrystalline body made of an ultra thin line with a fine diameter, whicha conventional etching technique could not provide, and to obtain anovel production method thereof. Another object of the invention is toprovide a ring crystalline body capable of reliably providing electricconductivity along the ring even if it is a low-dimensional conductorand a production method thereof.

[0012] In order to achieve these objects, a first aspect of the presentinvention provides a ring crystalline body comprising circularlycontinuous crystalline transition metal dichalcogenide or transitionmetal trichalcogenide.

[0013] Further, a second aspect of the present invention provides a ringcrystalline body comprising a circularly continuous crystallinelow-dimensional conductor.

[0014] The foregoing transition metal dichalcogenide or transition metaltrichalcogenide includes, for example, NbSe₃, NbSe₂, TaSe₃, TaSe₂, TaS₂,MoS₂, and the like. These NbSe₃, NbSe₂, TaSe₃, TaSe₂, TaS₂, MoS₂, andthe like are also low-dimensional conductors.

[0015] The ring crystalline body comprising these materials has atotally novel structure body. Such a transition metal dichalcogenide, atransition metal trichalcogenide, or a low-dimensional conductorincludes a superconductive material. A ring crystalline body comprisinga superconductive material or the like may be used, for example, as anelement of a SQUID in an optional shape. In the case of a circularshape, the ring crystalline body makes it possible to precisely measurea scarce signal emitted out a living thing and a living body and is thusextremely useful.

[0016] Further, when a large number of the ring crystalline bodies arepartly cut and joined in a spring-like shape, a nano-spring can beobtained and further, since the ring crystalline body made of the abovedescribed materials can generate an intense magnetic field in a narrowregion, if a plurality of the ring crystalline bodies are joined to be acoil-like shape, a nano-actuator can be produced. Besides, a nano-ballbearing can be produced by disposing the ring crystalline bodies double.

[0017] In addition to those, the ring crystalline body can be used for aquantum computer, an ultrafine battery utilizing inter-current function,a memory based on permanent current and the like and applicable to awide range of the application fields and remarkably useful in theindustrial sphere.

[0018] The shape of the ring crystalline body is approximately circularor elliptical and the size is preferably approximately 0.1 to 10 μm inthe diameter in the case of the circular shape and in the major axis inthe case of the elliptical shape and several to several tens nm in theline width.

[0019] Preferably, the crystallinity is a single crystal. Even in thecase the ring crystalline body is of a low-dimensional conductor, if thecrystallinity is a single crystal, electric conductivity is obtainedalong the ring, so that the ring crystalline body can be used as anelement of a SQUID and its application fields are widened.

[0020] In order to produce such an ultrafine ring crystalline body,another aspect of the invention provides a novel production method ofthe ring crystalline body comprising steps of forming a continuous ordiscontinuous underlayer ring having an ultrafine three-dimensionalstructure in the substrate surface and circularly growing a crystalalong the underlayer ring.

[0021] Usable for the material of the substrate is glass, quartz,silicon, diamond, sapphire, and the like.

[0022] Further, the underlayer ring is to be a point of starting thegrowth of the crystal and preferably a ring composed of solelycontinuously circular particles of elements composing the crystal to begrown thereafter or a ring composed of a large number of fine particlescomprising the elements arranged discontinuously and circularly.Alternatively, the particles and ultrafine particles may be of elementscompletely different from those composing the crystal. Even in the caseof ultrafine particles of elements different from those of the crystal,these ultrafine particles are not diffused in the crystal and do notbecome contaminant substances in the crystal.

[0023] According to such a method, it is made possible to produce a ringcrystalline body with a size as extremely fine as 0.1 to 10 μm diameterand 10 nm line width, which is impossible to be produced by aconventional method. Further, the production speed is high and massproduction at a high efficiency on the bases of industrial scale can bealso possible. Moreover, since no costly apparatus is required, aneconomical product can be provided.

[0024] Further, regarding the formed ring crystalline body, those withany optional diameter size can be produced by changing the size of theunderlayer ring, and the line width and the thickness of a ringcrystalline body can optionally be adjusted by controlling the growth ofthe crystal. Moreover, a ring crystalline body can be formed into atubular shape by increasing the thickness of the ring crystalline body.

[0025] Further, since the ring crystalline body is made of a singlecrystal, even if the crystal is, for example, a low-dimensionalconductor, electric current flows along the ring and therefore, the ringcrystalline body can be used as a material for a SQUID.

[0026] Incidentally, this method can make it possible to produce notonly a ring crystalline body comprising the transition metaldichalcogenides, transition metal trichalcogenide, and low-dimensionalconductors, but also a ring crystalline body comprising other metalmaterials and organic materials.

[0027] Preferably, the underlayer ring is formed by sticking droplets ofan underlayer ring material to the substrate surface and evaporating thedroplets.

[0028] The method for sticking droplets to the substrate surfaceincludes a method sticking droplets of an underlayer material byevaporation and a method comprising the steps of putting an ultrafineunderlayer material on the substrate surface by atomic tweezers,liquefying the underlayer material by heating the substrate, andevaporating the liquefied droplets.

[0029] Such droplets become approximately perfectly circular in thesubstrate surface and are evaporated by heating to leave ultrafineparticles in the circumferential parts of the approximately perfectlycircular shape. The materials of the droplets may properly be selectedtaking their wettability to the substrate and their surface tension intoconsideration.

[0030] The size of the underlayer ring is determined by the size of thedroplets and for example, in the case droplets of an underlayer materialare stuck to the substrate surface by evaporation, the size of thedroplets can be controlled by the supply amount of the underlayermaterial to be evaporated and the temperature of the substrate. Thediameter of the droplets is preferably set to be within a range from 0.1to 10 μm.

[0031] As the underlayer material, constituent elements of a crystal tobe grown can be used, however it is not limited to them. For example, inthe case of producing a ring crystalline body comprising a transitionmetal dichalcogenide or a transition metal trichalcogenide, chalcogenelements which are contained in the crystalline body or chalcogenelements which are not contained in the crystalline body may be used forthe underlayer material. Further other materials, for example, aninorganic material such as Al₂O₃, MoS₂ and the like, and an organicmaterial can be used for the underlayer material.

[0032] Incidentally, in the case the underlayer ring is required to beapproximately elliptical shape, for example, by using a Ni type magneticmaterial as the underlayer material and applying an electric field or amagnetic field to the droplets, the upper face shapes of the dropletscan be formed to be elliptical and by evaporating the droplets in such astate, an approximately elliptical underlayer ring can be produced.

[0033] Further, if a plurality of droplets are stuck to the substratesurface while neighboring one another, underlayer rings with a shapecomposed of a plurality of circles adjoined to one another can be formedto make it possible to produce a plurality of ring crystalline bodiesadjoined to each other along the underlayer rings.

[0034] Also preferably, the crystal is grown by evaporation or bysputtering.

[0035] Means for, for example, thermal CVD and plasma CVD may beemployed for the evaporation and a technique conventionally well-knownas a film formation technique in the semiconductor fabrication can beemployed.

[0036] Various conditions at the time of crystal growth, the temperatureof the substrate, the flow rate of raw materials and the like in thecase of evaporation are controlled, so that the line width and thicknessof the ring crystalline bodies to be obtained can freely be controlledand further the crystal structure can also be freely controlled and ringcrystalline bodies of a single crystal can be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIGS. 1A and 1B schematically show a production method of anunderlayer ring in a production method of a ring crystalline bodyaccording to the present invention.

[0038]FIGS. 2A and 2B schematically show a production method of anunderlayer ring in the production method of a ring crystalline bodyaccording to the present invention.

[0039]FIG. 3 is an electron microscopic photograph of a ring crystallinebody of NbSe₃, which is a preferable example of the present invention.

[0040]FIG. 4 is an electron microscopic photograph of a ring crystallinebody in an 8-shape form, which is another preferable example of thepresent invention.

[0041]FIG. 5 is an electron microscopic photograph of a ring crystallinebody in a tubular form, which is the other preferable example of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Hereinafter, a production method of a ring single crystal bodyaccording to an embodiment of the present invention will be specificallydescribed with reference to the accompanying drawings.

[0043]FIG. 1 and FIG. 2 are illustrations schematically showing aproduction method of an underlayer ring.

[0044] At first, droplets 2 of the underlayer material is evaporated ona surface 1 a of a substrate 1 and stuck to it. The side view of thedroplet 2 at that time and a top plan view thereof are respectivelyillustrated in FIG. 1A and in FIG. 1B. Since the surface tension of thedroplets 2 is changed according to the temperature of the substrate 1,the diameter size of the droplets 2 can be controlled by the temperatureof the substrate 1. The pressure at that time is so controlled to be atthe vacuum degree at which the droplets and the equilibrium vaporpressure are kept.

[0045] Further, the droplets 2 are heated by increasing the temperatureof the substrate 1 bearing the droplets 2 to evaporate droplets 2. Aside view of the substrate 1 after the evaporation is illustrated inFIG. 2A and a top plan view thereof is illustrated in FIG. 2B. When thedroplets 2 of the underlayer material are evaporated, the underlayermaterial becomes an inorganic polymer during the melting and aftermelting and a large number of fine particles 3a are discontinuouslycircularly arranged along the circumferences of the droplets 2 to forman underlayer ring 3.

[0046] The substrate 1 having the underlayer ring 3 formed is thensubjected to a conventionally known treatment such as evaporation orsputtering to produce a ring crystalline body with crystallineproperties along the underlayer ring 3. At that time, the conditions ofevaporation or sputtering are properly set, so that a ring crystallinebody of a single crystal or a polycrystal can be obtained.

[0047] Hereinafter, the present invention will be described according tospecific examples given below.

EXAMPLE 1

[0048] A droplet of Se as an underlayer material was stuck to thesurface of a glass substrate by evaporation. The substrate temperaturewas set to be about 300° C. and the vacuum degree was set to be about133 to 1330 Pa at that time. When the temperature of the substrate washeated up to 600° C. to evaporate the droplet, an approximatelyperfectly circular underlayer ring with the diameter of 300 nm to 500 μmwas formed.

[0049] When the substrate having the underlayer ring formed in such amanner was heated in a tubular quartz furnace at 700 to 800° C. whileraw material gas (NbSe₃) being passed through the furnace to carry outevaporation, a crystal of NbSe₃ was grown circularly along theunderlayer ring and a ring crystalline body was produced. An electronmicroscope photograph is shown in FIG. 3.

[0050] The ring crystalline body of NbSe₃ was observed by x-raydiffraction and electron beam diffraction to find it was a singlecrystal. Further, an investigation carried out into the electricconduction made it clear that electric conduction along the ring wasobtained. Further, in the case the ring crystalline body of NbSe₃ wasfurther converted to be a superconductor and used as a SQUID element, itwas supposed to be possible to obtain a highly capable SQUID.

[0051] Further, in the case of using S type TaS₃ and NbS₃ and Te typeNbTe₃, and TaTe₃ in place of the Se for the underlayer material toproduce an underlayer ring in the same manner as that in case of usingSe and to carry out evaporation of NbSe₃ on the underlayer ring in theabove described conditions, a ring crystalline body of the same singlecrystal as that of the case using Se was obtained.

EXAMPLE 2

[0052] In the same evaporation conditions as those of the example 1,droplets of Se and Ni were stuck to the substrate surface as underlayermaterials. After that, if the droplets were evaporated in the sameconditions as those of the example 1 while an electric field or amagnetic field being applied to the droplets, an underlayer ring withapproximately elliptical shape was formed. When NbSe₃ was evaporated inthe underlayer ring with the elliptical shape, a ring crystalline bodywith an approximately elliptical shape was obtained. The observation ofthe crystalline body by an x-ray diffraction and an electron beamdiffraction made it clear that the obtained crystalline body was of asingle crystal. Further, the electric conduction along the ellipticalshape was obtained.

EXAMPLE 3

[0053] Two droplets of Se as a underlayer raw material were stuck to thesurface of a glass substrate while being adjoined to each other in thesame evaporation conditions as those of the example 1. After that, anunderlayer ring in an approximately 8-shape form in which two circlesare adjoined to each other was formed by carrying out evaporation ofdroplets in the same conditions as those of the example 1. While theunderlayer ring being floated in vacuum in form of a twistedapproximately 8-shape, NbSe₃ was evaporated to obtain a continuouscrystalline body composed of two circular crystalline bodies adjoined toeach other in form of a twisted approximately 8-shape. An electronmicroscopic photograph of the crystalline body is shown in FIG. 4. Theobservation of the crystalline body by x-ray diffraction and electronbeam diffraction made it clear that the crystalline body with 8-shapedform was of a solely single crystal. Further, the electric conductioncontinuous along the 8-shaped form was obtained.

EXAMPLE 4

[0054] An underlayer ring of Se in an approximately perfect circle shapeof 300 nm to 500 μm diameter was formed on a glass substrate in the sameconditions as those of the example 1. When the substrate having theunderlayer ring formed was heated in a tubular quartz furnace at 700 to800° C. while NbSe₂ being passed through the furnace to carry outevaporation, a crystal of NbSe₂ was grown circularly along theunderlayer ring and a ring crystalline body was produced.

[0055] The observation of the crystalline body of NbSe₂ by x-raydiffraction and electron beam diffraction made it clear that thecrystalline body was a single crystal. Further, the investigation intothe electric conduction made it clear that the electric conduction alongthe circular shape was obtained. Further, in the case the ringcrystalline body of NbSe₂ was further converted to be a superconductorand used as a SQUID element, it was supposed to be possible to obtain ahighly capable SQUID.

EXAMPLE 5

[0056] An underlayer ring in an approximately perfect circle shape wasformed on a glass substrate in the same conditions as those of theexample 1 and when the substrate having the underlayer ring formed washeated in a tubular quartz furnace at 700 to 800° C. while raw materialgas (NbSe₃) being passed through the furnace to carry out evaporation, acrystal of NbSe₃ was grown circularly along the underlayer ring and aring crystalline body was produced. When the NbSe₃ gas evaporation wascontinued, a tubular ring crystalline body was obtained. An electronmicroscopic photograph of the tubular ring crystalline body is shown inFIG. 5.

[0057] The observation of the tubular crystalline body of NbSe₃ by x-raydiffraction and electron beam diffraction made it clear that the tubularcrystalline body of NbSe₃ was a single crystal. Further, theinvestigation into the electric conduction made it clear that theelectric conduction along the circular shape was obtained.

[0058] The present invention was not at all limited to the abovedescribed examples and crystalline bodies in a twisted 8-shape form justlike so-called Mobius's strip and in a coil-like form can be obtained bychanging the various conditions at the time of the underlayer ringformation and evaporation.

[0059] Further, besides the above described transition metaldichalcogenide (MX₂) or transition metal trichalcogenide (MX₃), avariety of combinations of M and X wherein M=Nb, Ta, and Mo and X=S, Se,and Te are possible. Further, the ring crystalline bodies comprising avariety of types of organic materials can be produced.

What is claimed is:
 1. A ring crystalline body comprising a circularlycontinuous crystalline transition metal dichalcogenide or transitionmetal trichalcogenide.
 2. A ring crystalline body comprising acircularly continuous crystalline low-dimensional conductor.
 3. The ringcrystalline body according to claim 1 or claim 2, wherein thecrystallinity is a single crystal.
 4. A production method of a ringcrystalline body comprising the steps of: forming a continuous ordiscontinuous underlayer ring having an ultrafine three-dimensionalstructure in the substrate surface; and circularly growing a crystalalong the underlayer ring.
 5. The production method according to claim4, wherein the underlayer ring is formed by sticking droplets of anunderlayer ring material to the substrate surface and evaporating thedroplets.
 6. The production method according to claim 4, wherein thecrystal is grown by evaporation.
 7. The production method according toclaim 4, wherein the crystal is grown by sputtering.